Good Omens by Terry Pratchett and Neil Gaiman is an excellent book and stands as one of my favourite books. Different to the Disc World series but hugely funny.
Neil Gaiman is a good author but I don't find his books have the put down and pick back up a few weeks later that you are looking for.
+1 to Lee Child, he follows a formula but good read and could be put down and picked up later (although I struggle!).
Ian Rankin and the Rebus series, but word of warning start at the start as a lot of character development goes on in the series and its best to start early and go with the flow.
Stuart McBride and Cold Granite is a good read, but similar to Rebus series start at the start as character development means you sometimes may miss part of the narrative importance of bits if you start later in the series (they still make sense but small details are not there).
Will have a think and see what else comes to mind.
Here is the list of authors (and characters) that populate my Kindle:
Daniel Silve (Gabriel Alon) Alex Berenson (John Wells) Lee Child (Jack Reacher) James Twining (Tom Kirk) Nelson Demille (John Corey) David Baldacci (Shaw) Steve Berry (Cotton Malone) Jack Higgins (Sean Dillon) Robert Harris (Luke Kelso) Vince Flynn (Mitch Rapp) Noah Boyd (Steve Vail)
Now I won't list the titles, because I basically have all books for each series. And finished all of them... Google is your friend, most authors have a website or wikipedia page listing the titles in release order.
I've been reading a fair amount of Young Adult fiction lately (mostly on the recommendations of my wife who is a librarian and a blogger - check out her blog here http://gnomadiclibrarian.blogspot.com/). It's pretty good. In particular, I enjoyed Saci Lloyd's "Carbon Diaries" books, Charlie Higson's "The Enemy" and the sequel "The Dead", and Patrick Ness' Chaos Walking trilogy.
The Carbon Diaries are written in the first person about a young girl living in Britain in 2015 where they are introducing the Carbon Card, rationing each person's carbon use to 200 credits. It's a fascinating dystopian vision of people struggling to cope with radical change in their lives.
The Charlie Higson books are ostensibly "zombie" books, but have a lot more richness than that suggests. The central concept of the book is that a disease has ravaged Britain, and anyone older than 14 has been struck down and effectively zombified. Again, it's a fascinating insight into a world where there are no "grown-ups" and shows a bunch of kids stepping up (or not) to their new roles as leaders.
The Chaos Walking trilogy by Patrick Ness has to be among the best fiction I've read in a long while. It's about a society where there are no women any more, the men have "noise" (basically a form of telepathy) and wins my prize for best opening sentence in a fiction book "The first thing you find out when yer dog learns to talk is that dogs don't got nothing much to say." The story follows Todd, the youngest boy in the village who learns a disturbing secret about his society, and goes on the run. I found all three books in the series genuinely un-put-downable.
Though these books are ostensibly written for young adults, I found them to be easily as good as any "adult" fiction, not dumbed down in any way, and grappling with interesting and enjoyable takes on big issues. The blog I've linked to above should have reviews of most of these books (and many more besides), if you want to know more...